The actor explained that the show's creator Doug Ellin allowed him to keep the item, which Ari was given in the fifth season.
"Doug was kind enough to let me walk away with this fine watch that Ari Gold wore for a number of years," Piven told WENN. "And it's really, really beautiful."
Kevin Connolly, who plays Eric, also revealed that he has a souvenir from his time on the HBO series.
"I took my 'E' paperweight off my desk," he said. "Now I have it at my house."
Piven recently revealed that Ari will be "brought to his knees" during the series finale of Entourage, adding that the show "couldn't have ended better".
Entourage will come to a close after the eighth season, which is currently airing on Sundays at 10.30pm on HBO in the US and on Mondays at 10.50pm on Sky Atlantic in the UK.
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Watch Jeremy Piven and Rex Lee looking back on Entourage below: